fix: switch prefix ASCII input source on the foreground client (#1016)

* fix: switch prefix ASCII input source on the foreground client

The macOS prefix ASCII-switch ran in the headless server, whose
TISCopyCurrentKeyboardInputSource read is a stale per-process cache
(refreshed only via a main-run-loop notification the server never pumps),
so prefix could leave the terminal on the wrong input source.

Forward it to the foreground client, like clipboard: sync_prefix_input_source
emits AppEvent::PrefixInputSource as an intent; the server forwards it to the
foreground client and the monolithic app applies it in-process via
RealPrefixInputSource, which pumps its main run loop before the stale TIS read.
Key it on Mode::wants_ascii_input so multi-level prefix commands keep ASCII
until returning to the terminal, and restore the IME for rename text entry.

Adds ServerMessage::PrefixInputSource to the already-unreleased protocol 15.

refs #774

* fix: keep prefix input-source switch out of the headless server process

An App-internal drain (the exhaustive drain at the top of
handle_api_request, reachable from prefix-key runtime mutations) can
consume a queued PrefixInputSource intent before the server's
forwarding drain sees it, applying the TIS switch in the headless
server process and stranding the restore state. Gate the in-process
switch on App.local_input_source_switch, disabled by the headless
server alongside the other local side effects, so a swallowed intent
degrades to a skipped switch. Widen the forwarding-bypass maintenance
test to the handle_internal_event_with_prefix_sync wrapper.

refs #774

* docs: clarify prefix input-source comments and flag docs

refs #774

* fix: bump protocol for prefix input source

refs #774

---------

Co-authored-by: Ogulcan Celik <ogulcancelik@gmail.com>

3 files changed, 8 insertions, 8 deletions

diff --git a/tests/api_ping.rs b/tests/api_ping.rs
index 1d625637..24204548 100644
--- a/tests/api_ping.rs
+++ b/tests/api_ping.rs
@@ -304,7 +304,7 @@ fn ping_over_socket_returns_version() {
     assert_eq!(value["result"]["version"], env!("CARGO_PKG_VERSION"));
     // Intentionally hardcoded so wire protocol bumps require updating this test.
     // Changing this value means old clients/servers are no longer compatible.
-    assert_eq!(value["result"]["protocol"], 15);
+    assert_eq!(value["result"]["protocol"], 16);
 
     cleanup_spawned_herdr(child, base);
 }
diff --git a/tests/cli_wrapper.rs b/tests/cli_wrapper.rs
index d3f67780..eac0b376 100644
--- a/tests/cli_wrapper.rs
+++ b/tests/cli_wrapper.rs
@@ -1620,7 +1620,7 @@ fn status_commands_report_client_and_server_versions() {
         "stdout: {full_stdout}"
     );
     assert!(
-        full_stdout.contains("  protocol: 15"),
+        full_stdout.contains("  protocol: 16"),
         "stdout: {full_stdout}"
     );
     assert!(full_stdout.contains("server:\n"), "stdout: {full_stdout}");
@@ -1653,7 +1653,7 @@ fn status_commands_report_client_and_server_versions() {
         "stdout: {server_stdout}"
     );
     assert!(
-        server_stdout.contains("protocol: 15"),
+        server_stdout.contains("protocol: 16"),
         "stdout: {server_stdout}"
     );
 
@@ -1665,7 +1665,7 @@ fn status_commands_report_client_and_server_versions() {
         "stdout: {client_stdout}"
     );
     assert!(
-        client_stdout.contains("protocol: 15"),
+        client_stdout.contains("protocol: 16"),
         "stdout: {client_stdout}"
     );
     assert!(
@@ -1675,7 +1675,7 @@ fn status_commands_report_client_and_server_versions() {
 
     let full_json = run_cli_json(&socket_path, &["status", "--json"]);
     assert_eq!(full_json["client"]["version"], env!("CARGO_PKG_VERSION"));
-    assert_eq!(full_json["client"]["protocol"], 15);
+    assert_eq!(full_json["client"]["protocol"], 16);
     assert_eq!(full_json["server"]["status"], "running");
     assert_eq!(full_json["server"]["running"], true);
     assert_eq!(full_json["server"]["compatible"], true);
@@ -1689,12 +1689,12 @@ fn status_commands_report_client_and_server_versions() {
     let server_json = run_cli_json(&socket_path, &["status", "server", "--json"]);
     assert_eq!(server_json["status"], "running");
     assert_eq!(server_json["version"], env!("CARGO_PKG_VERSION"));
-    assert_eq!(server_json["protocol"], 15);
+    assert_eq!(server_json["protocol"], 16);
     assert_eq!(server_json["compatible"], true);
 
     let client_json = run_cli_json(&socket_path, &["status", "client", "--json"]);
     assert_eq!(client_json["version"], env!("CARGO_PKG_VERSION"));
-    assert_eq!(client_json["protocol"], 15);
+    assert_eq!(client_json["protocol"], 16);
     assert!(client_json["binary"]
         .as_str()
         .is_some_and(|path| !path.is_empty()));
diff --git a/tests/support/mod.rs b/tests/support/mod.rs
index 5844bfa7..e4a9139a 100644
--- a/tests/support/mod.rs
+++ b/tests/support/mod.rs
@@ -15,7 +15,7 @@ static INIT: Once = Once::new();
 static CLEANUP_GUARD: OnceLock<CleanupGuard> = OnceLock::new();
 const WATCHDOG_SCAN_INTERVAL: Duration = Duration::from_secs(1);
 const RUNTIME_OWNER_MARKER: &str = ".herdr-test-owner-pid";
-pub const CURRENT_PROTOCOL: u32 = 15;
+pub const CURRENT_PROTOCOL: u32 = 16;
 
 pub fn register_spawned_herdr_pid(pid: Option<u32>) {
     let Some(pid) = pid else {